Light emitting device, display unit, and illumination unit

ABSTRACT

A light emitting device of the disclosure includes a first light source and a second light source; a light-guiding plate having a first main surface and a second main surface that face each other, a first end surface facing the first light source, and a second end surface facing the first end surface and the second light source; a prism sheet disposed to face the first main surface; and a reflection sheet disposed to face the second main surface. The light-guiding plate includes a plurality of first slope sections and a plurality of second slope sections both provided on one of the first main surface and the second main surface, in which the plurality of first slope sections are provided to allow the light-guiding plate to be thinner in a first direction that extends from the first end surface to the second end surface, and the plurality of second slope sections are provided to allow the light-guiding plate to be thicker in the first direction, and each provided alternately with each of the first slope sections in the first direction. A proportion of area occupied by the second slope sections increases in a predetermined range from the second end surface, as a distance from the second end surface increases.

TECHNICAL FIELD

The disclosure relates to a light emitting device that makes it possibleto change directivity of light to go out, a display unit having such alight emitting device, and an illumination unit.

BACKGROUND ART

For example, some of liquid crystal display units have a backlight thatis able to change directivity of light. For example, PTL 1 and PTL 2each disclose a liquid crystal display unit including a first lightsource, a second light source, a first light-guiding plate, and a secondlight-guiding plate. The first light-guiding plate guides light goingout from the first light source to a liquid crystal panel. The secondlight-guiding plate guides light going out from the second light sourceto the liquid crystal panel. In addition, PTL 3 discloses a liquidcrystal display unit including one light-guiding plate and two lightsources. In these liquid crystal display units, directivity of lightchanges between a case where the first light source emits light and acase where the second light source emits light. It is possible to applysuch a liquid crystal display unit to, for example, a car navigationsystem or a stereoscopic display unit.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. H11-273438

PTL 2: Japanese Unexamined Patent Application Publication No.2013-137388

PTL 3: Japanese Unexamined Patent Application Publication No. 2014-56201

SUMMARY OF THE INVENTION

Such a liquid crystal display unit, for example, narrows a range oflight-outgoing directions (increases directivity) in one mode, and widenthe range of light-outgoing directions (decreases directivity of light)in another mode. At the time, it is desirable that distribution ofluminance be desirably uniform.

It is therefore desirable to provide a light emitting device, a displayunit, and an illumination unit that make it possible to enhanceuniformity of luminance distribution.

A light emitting device according to one embodiment of the disclosureincludes a first light source and a second light source, a light-guidingplate, a prism sheet, and a reflection sheet. The light-guiding platehas a first main surface and a second main surface that face each other,a first end surface facing the first light source, and a second endsurface facing the first end surface and the second light source. Theprism sheet is disposed to face the first main surface. The reflectionsheet is disposed to face the second main surface. The light-guidingplate includes a plurality of first slope sections and a plurality ofsecond slope sections both provided on one of the first main surface andthe second main surface, in which the plurality of first slope sectionsare provided to allow the light-guiding plate to be thinner in a firstdirection that extends from the first end surface to the second endsurface, and the plurality of second slope sections are provided toallow the light-guiding plate to be thicker in the first direction, andeach provided alternately with each of the first slope sections in thefirst direction. A proportion of area occupied by the plurality ofsecond slope sections increases in a predetermined range from the secondend surface, as a distance from the second end surface increases.

A display unit according to one embodiment of the disclosure includes aliquid crystal display section, and a light-emission section. Thelight-emission section is disposed on a back surface side of the liquidcrystal display section. The light-emission section includes a firstlight source and a second light source, a light-guiding plate, a prismsheet, and a reflection sheet. The light-guiding plate has a first mainsurface and a second main surface that face each other, a first endsurface facing the first light source, and a second end surface facingthe first end surface and the second light source. The prism sheet isdisposed to face the first main surface. The reflection sheet isdisposed to face the second main surface. The light-guiding plateincludes a plurality of first slope sections and a plurality of secondslope sections both provided on one of the first main surface and thesecond main surface, in which the plurality of first slope sections areprovided to allow the light-guiding plate to be thinner in a firstdirection that extends from the first end surface to the second endsurface, and the plurality of second slope sections are provided toallow the light-guiding plate to be thicker in the first direction, andeach provided alternately with each of the first slope sections in thefirst direction. A proportion of area occupied by the plurality ofsecond slope sections increases in a predetermined range from the secondend surface, as a distance from the second end surface increases.

An illumination unit according to one embodiment of the disclosureincludes the above-described light emitting device.

In the light emitting device, the display unit, and the illuminationunit according to the respective embodiments of the disclosure, a ray oflight emitted from the first light source enters the first end surfaceof the light-guiding plate in a case where the first light source emitslight, whereas a ray of light emitted from the second light sourceenters the second end surface of the light-guiding plate in a case wherethe second light source emits light. Further, these rays of light gofrom the first main surface to outside through the prism sheet. On oneof the first main surface and the second main surface of thelight-guiding plate, the first slope sections and the second slopesections are provided in such a manner that the proportion of the areaoccupied by the plurality of second slope sections increases in thepredetermined range from the second end surface, as the distance fromthe second end surface increases.

According to the light emitting device, the display unit, and theillumination unit in the respective embodiments of the disclosure, theproportion of the area occupied by the plurality of second slopesections increases in the predetermined range from the second endsurface, as the distance from the second end surface increases. It istherefore possible to enhance uniformity of luminance distribution. Itis to be noted that the effects described above are not necessarilylimitative, and any of effects described in the disclosure may beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a configuration example of a lightemitting device according to a first embodiment of the disclosure.

FIG. 2 is an explanatory diagram illustrating a configuration example ofa light-guiding plate illustrated in FIG. 1.

FIG. 3 is a cross-sectional view of the configuration example of thelight-guiding plate illustrated in FIG. 2.

FIG. 4 is an explanatory diagram illustrating a certain parameter in thelight-guiding plate illustrated in FIG. 2.

FIG. 5 is an explanatory diagram illustrating another parameter in thelight-guiding plate illustrated in FIG. 2.

FIG. 6 is an explanatory diagram illustrating another parameter in thelight-guiding plate illustrated in FIG. 2.

FIG. 7 is another cross-sectional view illustrating the configurationexample of the light-guiding plate illustrated in FIG. 2.

FIG. 8 is an explanatory diagram illustrating another parameter in thelight-guiding plate illustrated in FIG. 2.

FIG. 9 is an explanatory diagram illustrating another parameter in thelight-guiding plate illustrated in FIG. 2.

FIG. 10 is a cross-sectional view of a configuration example of a prismsheet illustrated in FIG. 1.

FIG. 11 is an explanatory diagram illustrating a traveling direction oflight in the light-guiding plate illustrated in FIG. 1.

FIG. 12 is an explanatory diagram illustrating a traveling direction oflight in the prism sheet illustrated in FIG. 1.

FIG. 13 is a characteristic diagram illustrating viewing anglecharacteristics of the light emitting device illustrated in FIG. 1.

FIG. 14 is another characteristic diagram illustrating viewing anglecharacteristics of the light emitting device illustrated in FIG. 1.

FIG. 15 is another characteristic diagram illustrating viewing anglecharacteristics of the light emitting device illustrated in FIG. 1.

FIG. 16 is a table illustrating parameter examples of a light emittingdevice according to each reference example.

FIG. 17 is a perspective view of a configuration example of a lightemitting device according to a reference example.

FIG. 18 is a characteristic diagram illustrating viewing anglecharacteristics of the light emitting device according to the referenceexample.

FIG. 19 is another characteristic diagram illustrating viewing anglecharacteristics of the light emitting device according to the referenceexample.

FIG. 20 is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 21A is a characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 21B is another characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 22A is a characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 22B is another characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 23A is a characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 23B is another characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 24A is a characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 24B is another characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 25A is a characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 25B is another characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 26A is a characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 26B is another characteristic diagram illustrating distribution ofluminance according to another reference example.

FIG. 27 is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 28 is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 29A is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 29B is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 29C is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 29D is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 29E is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 29F is a characteristic diagram illustrating viewing anglecharacteristics of a light emitting device according to anotherreference example.

FIG. 30 is a perspective view of a configuration example of a lightemitting device according to a modification example.

FIG. 31 is a perspective view of a configuration example of a displayunit according to a second embodiment.

FIG. 32A is a perspective view of an appearance configuration of anelectronic book to which an embodiment is applied.

FIG. 32B is a perspective view of an appearance configuration of anotherelectronic book to which an embodiment is applied.

FIG. 33 is a perspective view of an appearance configuration of asmartphone to which an embodiment is applied.

FIG. 34 is a perspective view of an appearance configuration of anillumination unit to which an embodiment is applied.

MODES FOR CARRYING OUT THE INVENTION

Some embodiments of the disclosure will be described below in detail inthe following order, with reference to the drawings.

1. First Embodiment (A Light Emitting Device) 2. Second Embodiment (ADisplay Unit) 3. Application Examples 1. First Embodiment [ConfigurationExample]

FIG. 1 illustrates a configuration example of a light emitting device (alight emitting device 1) according to a first embodiment. The lightemitting device 1 is used, for example, as a backlight that illuminatesa transmission liquid-crystal display panel from behind, or as anillumination unit in a place such as a room. The light emitting device 1includes a plurality of light sources 10A, a plurality of light sources10B, a light-guiding plate 20, a reflection sheet 30, a prism sheet 40,and a diffusing sheet 50.

The light sources 10A and 10B are each a light source that outputs lightto the light-guiding plate 20, and are each configured of, for example,a light emitting diode (LED). The light source 10A is, for example,sealed in a package, and mounted on a light source substrate 12A. Theplurality of light sources 10A are arranged side by side in a Y-axisdirection (an up-down direction) and disposed to face a light enteringsurface 20A of the light-guiding plate 20. Similarly, the light source10B is, for example, sealed in a package, and mounted on a light sourcesubstrate 12B. The plurality of light sources 10B are arranged side byside in the Y-axis direction (the up-down direction) and disposed toface a light entering surface 20B of the light-guiding plate 20. A lightsource section including the plurality of light sources 10A and a lightsource section including the plurality of light sources 10B areconfigured to emit light individually. Specifically, the light emittingdevice 1 narrows a range of light-outgoing directions (increasesdirectivity) in a case where the plurality of light sources 10A emitlight, and widens the range of light-outgoing directions (decreasesdirectivity) in a case where the plurality of light sources 10B emitlight, as will be described later.

The light-guiding plate 20 guides light going out from the plurality oflight sources 10A and 10B to the prism sheet 40. The light-guiding plate20 mainly includes, for example, transparent thermoplastic resin such aspolycarbonate resin and acrylic resin (e.g., polymethyl methacrylate(PMMA). The light-guiding plate 20 is a substantially rectangularparallelepiped member having a pair of main surfaces (a front surfaceand a back surface) facing each other in a Z-axis direction (afront-back direction), and four end surfaces (side surfaces) linkingfour sides of one of the main surfaces to four sides of the other. Amongthe four end surfaces, two surfaces facing each other in an X-axisdirection (a lateral direction) are the light entering surfaces 20A and20B. The light entering surface 20A is a surface that faces theplurality of light sources 10A, and the light entering surface 20B is asurface that faces the plurality of light sources 10B. Further, of thepair of main surfaces, the front surface is a light outgoing surface20C, and the back surface is a light outgoing surface 20D. The lightoutgoing surface 20C is a surface that faces the prism sheet 40, and thelight outgoing surface 20D is a surface that faces the reflection sheet30. The light-guiding plate 20 guides light entering from the lightentering surface 20A to the light outgoing surface 20C, and guides lightentering from the light entering surface 20B to the light outgoingsurface 20C.

The light outgoing surface 20C (the front surface) of the light-guidingplate 20 has a lenticular shape as illustrated in FIG. 1. In otherwords, on the light outgoing surface 20C, lenses each having asubstantially semicircular cross-sectional shape in an YZ plane andextending in the X-axis direction are arranged side by side in theY-axis direction. Further, a plurality of prisms PA and PB are formed onthe light outgoing surface 20D (the back surface) of the light-guidingplate 20, as will be described below.

FIG. 2 illustrates the light-guiding plate 20. FIG. 3 illustrates aconfiguration example of the light outgoing surface 20D (the backsurface) of the light-guiding plate 20. Specifically, (A) of FIG. 3illustrates a shape of the light outgoing surface 20D in a portion W1illustrated in FIG. 2, (B) of FIG. 3 illustrates a shape of the lightoutgoing surface 20D in a portion W2 illustrated in FIG. 2, and (C) ofFIG. 3 illustrates a shape of the light outgoing surface 20D in aportion W3 illustrated in FIG. 2. In FIG. 3, inclinations and the likeare exaggerated for convenience of description.

In the light-guiding plate 20, the plurality of prisms PA extending inthe Y-axis direction are arranged side by side in the X-axis direction,over the entire light outgoing surface 20D. The prism PA has a ridge andtwo surfaces (a gentle slope PA1 and a steep slope PA2) provided withthe ridge in between. The ridge of the prism PA is formed to extend inthe Y-axis direction. The gentle slope PA1 is such a slope that thelight-guiding plate 20 becomes thinner in the X-axis direction. Thesteep slope PA2 is such a slope that the light-guiding plate 20 becomesthicker in the X-axis direction. A level of inclination in the steepslope PA2 is greater than a level of inclination in the gentle slopePA1. In this way, the plurality of prisms PA are formed in a stair-likeshape on the light outgoing surface 20D of the light-guiding plate 20.

In this example, the prisms PA have respective widths LA equal to oneanother. Specifically, the width LA may be, for example, 0.2 [mm]. Inaddition, an inclination angle (a gentle slope angle θ1) of the gentleslope PA1, an inclination angle (a steep slope angle θ2) of the steepslope PA2, and a height HA (a height difference of the steep slope PA2)of the prism PA change depending on X-axis coordinates in thelight-guiding plate 20, as will be described below.

FIG. 4 illustrates the gentle slope angle θ1 of the gentle slope PA1,and FIG. 5 illustrates the height HA of the prism PA. In these figures,a horizontal axis indicates a distance (coordinates) from a center inthe lateral direction of the light-guiding plate 20, when viewed fromthe back-surface side of the light-guiding plate 20. In other words, inFIGS. 4 and 5, the closer to left, the closer to the light enteringsurface 20B, whereas the closer to right, the closer to the lightentering surface 20A. In these figures, portions corresponding to theportions W1 to W3 illustrated in FIG. 2 are marked for convenience ofdescription. It is to be noted that the steep slope angle θ2 is 49degrees—θ1, in this example. In other words, the steep slope angle θ2 isabout 49 degrees.

Except for a portion in proximity to the light entering surface 20A (aright end), the height HA of the prism PA gradually increases as adistance from the light entering surface 20B (a left end) increases, asillustrated in FIG. 5. In contrast, the gentle slope angle θ1 graduallydecreases as illustrated in FIG. 4. The widths LA of the respectiveprisms PA are equal to one another, and the steep slope angle θ2 isabout 49 degrees and substantially uniform. Hence, an area proportion ofthe steep slope PA2 in the prism PA gradually increases, as the distancefrom the light entering surface 20B (the left end) increases and as theheight HA of the prism PA increases. Further, in the portion inproximity to the light entering surface 20A (the right end), the heightHA is small, and the gentle slope angle θ1 is large.

FIG. 6 illustrates a thickness D of the light-guiding plate 20. In FIG.6, portions corresponding to the portions W1 to W3 illustrated in FIG. 2are marked for convenience of description. The thickness D of thelight-guiding plate 20 gradually increases from the light enteringsurface 20B (the left end) to a portion near the center and graduallydecreases from the portion near the center to the light entering surface20A (the right end), as illustrated in FIG. 6. The thickness D isslightly large near the light entering surface 20A (the right end). Inother words, the thickness D of the light-guiding plate 20 at the rightend and that at the left end of each of the prisms PA are notnecessarily the same. Hence, the thickness D of the light-guiding plate20 changes depending on the X-axis coordinates. Specifically, in a rangefrom the light entering surface 20B (the left end) to the portion nearthe center, the thickness D of the light-guiding plate 20 graduallyincreases, because the height HA of the prism PA is small (FIG. 5) andthe proportion of the steep slope PA2 in each of the prisms PA is small.Further, in a range from the portion near the center to the lightentering surface 20A (the right end), the thickness D of thelight-guiding plate 20 gradually decreases, because the height HA of theprism PA is large (FIG. 5) and the proportion of the steep slope PA2 inthe prism PA is large.

In addition, in the light-guiding plate 20, the prism PB is formed oneach of the gentle slopes PA1, in a portion (for example, the portionW3) which is in proximity to the light entering surface 20A of the lightoutgoing surface 20D as illustrated in FIGS. 2 and 3. In this example,the one prism PB is formed near a center of each of the gentle slopesPA1.

FIG. 7 illustrates a configuration example of the prism PB. The prism PBhas a ridge and two surfaces (a gentle slope PB1 and a steep slope PB2)provided with the ridge in between. The ridge of the prism PB is formedto extend in the Y-axis direction. The gentle slope PB1 is such a slopethat the light-guiding plate 20 becomes thinner in the X-axis direction.The steep slope PB2 is such a slope that the light-guiding plate 20becomes thicker in the X-axis direction. A level of inclination in thesteep slope PB2 is greater than a level of inclination in the gentleslope PB1. In addition, the level of inclination in the gentle slope PB1of the prism PB is greater than the level of inclination in the gentleslope PA1 of the prism PA. An inclination angle (a gentle slope angleθ3) of the gentle slope PB1, an inclination angle (a steep slope angleθ4) of the steep slope PB2, a width LB of the prism PB, and a height HB(a height difference of the steep slope PB2) of the prism PB changedepending on the X-axis coordinates in the light-guiding plate 20, aswill be described below.

FIG. 8 illustrates the gentle slope angle θ3 of the gentle slope PB1.FIG. 9 illustrates a proportion (an area ratio S) of the gentle slopePB1 of the prism PB in the gentle slope PA1 of the prism PA. It is to benoted that, in this example, the steep slope angle θ4 is 49 degrees—θ3,the width LB corresponds to the area ratio S, and the height HBcorresponds to the angles θ3 and θ4 as well as the width LB.

In the portion in proximity to the light entering surface 20A (the rightend), the area ratio S of the prism PB increases as a distance to thelight entering surface 20A decreases, as illustrated in FIG. 9. Further,in the portion in proximity to the light entering surface 20A (the rightend), the gentle slope angle θ3 of the prism PB increases as thedistance to the light entering surface 20A decreases, as illustrated inFIG. 8. In other words, the prism PB is provided only in the portion inproximity to the light entering surface 20A (the right end), and becomeslarger as the distance to the light entering surface 20A decreases.

The prisms PA and PB may be generated by, for example, trimming a die ofthe light-guiding plate 20, and then transferring a shape thereof byinjection molding. The die of the light-guiding plate 20 is trimmedusing a single crystal diamond bit. It is to be noted that the value ofeach of the angles θ1 to θ4 described above is a mere example, and, forexample, unevenness substantially same as that of processing accuracymay occur. Specifically, in a case where a corner of each of the prismsPA and PB is a curved surface due to the incomplete transfer resultingfrom the injection molding, a portion of each of the gentle slopes PA1and PB1 and the steep slopes PA2 and PB2 is a curved surface. In thiscase, for example, the gentle slope angle θ1 may be an average value ofthe gentle slope angles θ1 in the gentle slope PA1. This holds true forthe angles θ2 to θ4.

In this way, the plurality of prisms PA and PB are formed on the lightoutgoing surface 20D (the back surface) of the light-guiding plate 20.The light emitting device 1 therefore narrows the range oflight-outgoing directions (increases the directivity) in a case wherethe plurality of light sources 10A emit light, and widens the range oflight-outgoing directions (decreases the directivity) in a case wherethe plurality of light sources 10B emit light, as will be describedlater.

The reflection sheet 30 (FIG. 1) is provided to face the light outgoingsurface 20D (the back surface) of the light-guiding plate 20, andreflects light going out from the light outgoing surface 20D of thelight-guiding plate 20. Specifically, the reflection sheet 30 returnslight, which leaks from the light outgoing surface 20D after enteringthe light-guiding plate 20 from the light sources 10A and 10B, to thelight-guiding plate 20. The reflection sheet 30 has, for example,functions such as reflection, diffusion, and scattering. This allows thereflection sheet 30 to increase luminance by efficiently utilizing lightfrom the light sources 10A and 10B.

The reflection sheet 30 is made of, for example, foamed polyethyleneterephthalate (PET), a silver vapor deposition film, a multilayeredreflection film, or white PET. To provide the reflection sheet with afunction of regular reflection (specular reflection), it is preferableto perform processing such as silver vapor deposition, aluminum vapordeposition, and multilayer film reflection on a surface of thereflection sheet 30. To provide the reflection sheet 30 with a minuteshape, the reflection sheet 30 may be integrally formed by a techniquesuch as hot pressing molding using thermoplastic resin and meltextrusion molding. Alternatively, for example, the reflection sheet 30may be formed by applying energy-ray (e.g., ultraviolet-ray) curableresin to a base made of a material such as PET and then transferring ashape to the energy-ray curable resin. Here, examples of thermoplasticresin include polycarbonate resin, acrylic resin such as polymethylmethacrylate resin (PMMA), polyester resin such as polyethyleneterephthalate, amorphous copolymerization polyester resin such as MS (acopolymer of methyl methacrylate and styrene), polystyrene resin, andpolyvinyl chloride resin. In addition, the base may be made of glass, ifthe shape is transferred to the energy-ray (e.g., ultraviolet-ray)curable resin.

The prism sheet 40 (FIG. 1) is a sheet on which a plurality of prisms Qare formed. The prism sheet 40 guides light going out from the lightoutgoing surface 20C (the front surface) of the light-guiding plate 20to the diffusing sheet 50. Of the prism sheet 40, a back surface is alight entering surface 40A, and a front surface is a light outgoingsurface 40B. The light entering surface 40A is a surface facing thelight outgoing surface 20C of the light-guiding plate 20, and theplurality of prisms Q are formed on the light entering surface 40A. Thelight outgoing surface 40B is a surface facing the diffusing sheet 50.The prism sheet 40 may be formed in a manner similar to the reflectionsheet 30. Specifically, the prism sheet 40 may be formed by, forexample, applying energy-ray (e.g., ultraviolet-ray) curable resin to abase made of a material such as PET and then transferring a prism shapeto the energy-ray curable resin. Alternatively, a base and a prism shapemay be integrally formed by a technique such as hot pressing moldingusing thermoplastic resin such as PC (polycarbonate).

FIG. 10 illustrates a configuration example of the light enteringsurface 40A (the back surface) of the prism sheet 40. In the prism sheet40, the plurality of prisms Q extending in the Y-axis direction arearranged side by side in the X-axis direction, over the entire lightentering surface 40A. The plurality of prisms Q each have asubstantially triangular cross-sectional shape in an XZ plane. The prismQ has a ridge and two surfaces QA and QB provided with the ridge inbetween. The ridge of the prism Q is formed to extend in the Y-axisdirection. The surface QA is such a surface that the prism sheet 40becomes thinner in the X-axis direction. The surface QB is such asurface that the prism sheet 40 becomes thicker in the X-axis direction.

To be more specific, the surface QA includes two surfaces QA1 and QA2 inorder from the ridge side. In this example, an angle θA1 between thesurface QA1 and a normal (the Z-axis) of the prism sheet 40 is 34degrees, and the surface QA1 has a width of 9 [μm] in the X-axisdirection. In addition, in this example, an angle θA2 between thesurface QA2 and the normal of the prism sheet 40 is 30 degrees, and asurface QB1 has a width of 6.7 [μm] in the X-axis direction. Similarly,to be more specific, the surface QB includes three surfaces, which aresurfaces QB1, QB2, and QB3 in order from the ridge side. In thisexample, an angle θB1 between the surface QB1 and the normal of theprism sheet 40 is 37 degrees, and the surface QB1 has a width of 6 [μm]in the X-axis direction. In addition, in this example, an angle θB2between the surface QB2 and the normal of the prism sheet 40 is 29degrees, and the surface QB2 has a width of 4.5 [μm] in the X-axisdirection. Moreover, in this example, an angle θB3 between the surfaceQB3 and the normal of the prism sheet 40 is 23 degrees, and the surfaceQB3 has a width of is 3.8 [μm] in the X-axis direction.

In this way, the prism Q has an asymmetry shape in the X-axis direction.In addition, the angle changes by four degrees (=34−30) on the surfaceQA, and the angle changes by 14 degrees (=37−23) on the surface QB.Thus, in the prism Q, the change of the angle on the surface QB isgreater than the change of the angle on the surface QA. Hence, the lightemitting device 1 narrows the range of light-outgoing directions(increases the directivity) in a case where the plurality of lightsources 10A emit light, and widens the range of light-outgoingdirections (decreases the directivity) in a case where the plurality oflight sources 10B emit light, as will be described later.

The diffusing sheet 50 is a sheet that diffuses light going out from thelight outgoing surface 40B of the prism sheet 40, and includes, forexample, a microlens array (MLA). For example, the light emitting device1 improves viewing angle characteristics owing to the provision of thediffusing sheet 50, when causing the plurality of light sources 10B toemit light and widening the range of light-outgoing directions(decreases the directivity), as will be described later.

Here, the light source 10A corresponds to a specific example of a “firstlight source” in the disclosure, and the light source 10B corresponds toa specific example of a “second light source” in the disclosure. Thelight entering surface 20A corresponds to a specific example of a “firstend surface” in the disclosure, and the light entering surface 20Bcorresponds to a specific example of a “second end surface” in thedisclosure. The light outgoing surface 20C corresponds to a specificexample of a “first main surface” in the disclosure, and the lightoutgoing surface 20D corresponds to a specific example of a “second mainsurface” in the disclosure. The gentle slope PA1 corresponds to aspecific example of a “first slope section” in the disclosure, and thesteep slope PA2 corresponds to a specific example of a “second slopesection” in the disclosure. The gentle slope PB1 corresponds to aspecific example of a “third slope section” in the disclosure, and thesteep slope PB2 corresponds to a specific example of a “fourth slopesection” in the disclosure. The surface QB corresponds to a specificexample of a “first surface” in the disclosure, and the surface QAcorresponds to a specific example of a “second surface” in thedisclosure.

[Operation and Workings]

Next, operation and workings of the light emitting device 1 of thepresent embodiment will be described.

(Outline of Overall Operation)

First, outline of overall operation of the light emitting device 1 willbe described with reference to FIG. 1, etc. The plurality of lightsources 10A and 10B output light. The light-guiding plate 20 guideslight going out from the plurality of light sources 10A and 10B, to theprism sheet 40. The reflection sheet 30 reflects light going out fromthe light outgoing surface 20D (the back surface) of the light-guidingplate 20. The prism sheet 40 guides light going out from the lightoutgoing surface 20C of the light-guiding plate 20, to the diffusingsheet 50. The diffusing sheet 50 diffuses light going out from the lightoutgoing surface 40B of the prism sheet 40.

(Workings of Light-Guiding Plate 20)

The light-guiding plate 20 guides light going out from the plurality oflight sources 10A and 10B, to the prism sheet 40. At the time, the lightemitting device 1 narrows the range of light-outgoing directions(increases the directivity) in a case where the plurality of lightsources 10A emit light, and widens the range of light-outgoingdirections (decreases the directivity) in a case where the plurality oflight sources 10B emit light, as will be described below. The lightemitting device 1 narrows and widens the range of light-outgoingdirections, by using the plurality of prisms PA and PB formed on thelight outgoing surface 20D (the back surface) of the light-guiding plate20.

FIG. 11 illustrates an example of a light ray in the light-guiding plate20. In this example, behavior in the portion near the center of thelight-guiding plate 20 is illustrated. Only the prisms PA are formed inthis portion. Light LA going out from the light source 10A and light LBgoing out from the light source 10B will each be described below as anexample.

In a case where the light source 10A emits light, the light LA going outfrom the light source 10A first enters the light-guiding plate 20 fromthe light entering surface 20A. Upon entering the light-guiding plate20, the light LA travels while repeating reflection between the lightoutgoing surface 20C (the front surface) and the gentle slope PA1 of thelight outgoing surface 20D (the back surface), as illustrated in FIG.11. At the time, a traveling direction (a traveling angle) of the lightLA gradually changes, because the gentle slope PA1 has an inclination.As a result, an incident angle at the light outgoing surface 20C changeseach time the reflection occurs. After such repeats of reflection, thelight LA goes out from the light outgoing surface 20C (the frontsurface) in a direction deviating from a normal direction (the Z-axisdirection) of the light outgoing surface 20C, when the incident angle atthe light outgoing surface 20C falls within a predetermined angle range.In this way, the range of light-outgoing directions of the light LAgoing out from the light-guiding plate 20 narrows in a case where thelight source 10A emits light.

On the other hand, in a case where the light source 10B emits light, thelight LB going out from the light source 10B first enters thelight-guiding plate 20 from the light entering surface 20B.Subsequently, light LB1, which is a portion of the light LB entering thelight-guiding plate 20, is, for example, reflected at the steep slopePA2 of the light outgoing surface 20D (the back surface). The light LB1then goes out from the light outgoing surface 20C (the front surface) ina direction close to the normal direction (the Z-axis direction) of thelight outgoing surface 20C. Further, for example, light LB2 that isanother portion of the light entering the light-guiding plate 20 passesthrough the steep slope PA2 of the light outgoing surface 20D (the backsurface), following which the light LB2 is subsequently reflected offthe reflection sheet 30 and then enter the light-guiding plate 20 again.Afterward, the light LB2 goes out from the light outgoing surface 20C(the front surface), in a direction deviating from the normal direction(the Z-axis direction) of the light outgoing surface 20C. In this way,in a case where the light source 10B emits light, the range oflight-outgoing directions of the light LB going out from thelight-guiding plate 20 widens.

It is to be noted that although the workings of the prism PA aredescribed in this example, similar workings apply to the prism PB aswell.

As described above, in the light-guiding plate 20, the plurality ofprisms PA and PB are provided on the light outgoing surface 20D (theback surface). It is therefore possible to narrow the range oflight-outgoing directions (increase the directivity) in a case where theplurality of light sources 10A emit light and to widen the range oflight-outgoing directions (decrease the directivity) in a case where theplurality of light sources 10B emit light.

(Workings of Prism Sheet 40)

The prism sheet 40 guides light going out from the light outgoingsurface 20C of the light-guiding plate 20, to the diffusing sheet 50. Atthe time, the light emitting device 1 narrows the range oflight-outgoing directions in a case where the plurality of light sources10A emit light (increases the directivity) and widens the range oflight-outgoing directions (decreases the directivity) in a case wherethe plurality of light sources 10B emit light, as will be describedbelow. The light emitting device 1 narrows and widens the range oflight-outgoing directions, by using the prisms Q each having theasymmetry shape in the X-axis direction.

FIG. 12 illustrates an example of a light ray in the prism sheet 40. Thelight LA going out from the light-guiding plate 20 in a case where thelight source 10A emits light and the light LB going out from thelight-guiding plate 20 in a case where the light source 10B emits lightwill each be described below as an example.

In a case where the light source 10A emits light, the light LA going outfrom the light-guiding plate 20 enters from the light entering surface40A of the prism sheet 40. The light LA is subsequently reflected at thesurface QA of the prism Q, following which the light LA goes out fromthe light outgoing surface 40B in a direction close to a normaldirection (the Z-axis direction) of the light outgoing surface 40B. Atthe time, even if outgoing directions of respective rays of the light LAgoing out from the light-guiding plate 20 are slightly different,traveling directions of the respective rays become closer to each otherbecause the rays are reflected at the surfaces QA1 and QA2 havingslightly different inclinations, as illustrated in FIG. 12.

Meanwhile, in a case where the light source 10B emits light, the lightLB going out from the light-guiding plate 20 enters from the lightentering surface 40A of the prism sheet 40. The light LB is thenreflected at the surface QB of the prism Q, and the reflected light LBgoes out in wide directions centered at the normal direction (the Z-axisdirection) of the light outgoing surface 40B. At the time, even ifoutgoing directions of respective rays of the light LB going out fromthe light-guiding plate 20 are the same, the rays of the light LB travelin directions that vary from point to point (the surfaces QB1 to QB3)where reflection occurs in the prism plane QB, as illustrated in FIG.12. As described above, the range of light-outgoing directions of thelight LB going out from the light-guiding plate 20 is wide in a casewhere the light source 10B emits light. A range of traveling directionsof the light LB is further increased by the prism sheet 40, and thus therange of light-outgoing directions of the light LB going out from thelight outgoing surface 40B of the prism sheet 40 further widens.

In this way, the plurality of prisms Q are provided on the lightoutgoing surface 40B (the back surface) in the prism sheet 40. It istherefore possible to narrow the range of light-outgoing directions(increase the directivity) in a case where the plurality of lightsources 10A emit light, and to widen the range of light-outgoingdirections (decrease the directivity) in a case where the plurality oflight sources 10B emit light.

(Viewing Angle Characteristics of Light Emitting Device 1)

FIG. 13 illustrates viewing angle characteristics of the light emittingdevice 1 in a case where the light source 10A emits light. FIG. 14illustrates viewing angle characteristics of the light emitting device 1in a case where the light source 10B emits light. In FIGS. 13 and 14, ahorizontal axis indicates a horizontal (lateral) observation angle, anda vertical axis indicates a vertical (up-down) observation angle. FIGS.13 and 14 each illustrate nine contour lines. A peak luminous intensityobserved in a direction, in which each of the horizontal observationangle and the vertical observation angle is zero degree, is divided intoten equal portions by the nine contour lines.

FIG. 15 illustrates viewing angle characteristics of the light emittingdevice 1. WHA and WVA represent viewing angle characteristics of thelight emitting device 1 in a case where the light source 10A emitslight. WHA indicates a horizontal viewing angle characteristic, and WVAindicates a vertical viewing angle characteristic. WHB and WVB representviewing angle characteristics of the light emitting device 1 in a casewhere the light source 10B emits light. WHB indicates a horizontalviewing angle characteristic, and WVB indicates a vertical viewing anglecharacteristic. In FIG. 15, a horizontal axis indicates an observationangle (the horizontal observation angle or the vertical observationangle), and a vertical axis indicates a normalized luminous intensity.The normalized luminous intensity is a luminous intensity having a peakvalue of 1.

As illustrated in FIGS. 13 to 15, luminance decreases as the horizontalobservation angle and the vertical observation angle deviate from zerodegree. At the time, it is possible to narrow the viewing angles in boththe horizontal and the vertical directions in a case where the lightsource 10A emits light as illustrated in FIG. 13. It is also possible towiden the viewing angles in both the horizontal and the verticaldirections in a case where the light source 10B emits light asillustrated in FIG. 14.

Next, workings of the present embodiment will be described using somereference examples.

FIG. 16 illustrates each of parameters in light emitting devices S0 toS5 according to six reference examples, together with each of parametersin the light emitting device 1. In FIG. 16, parameters surrounded by abold line are the same as the parameters of the light emitting device 1.The light emitting devices S0 to S5 will be described below in detail.

(Light Emitting Device S0)

FIG. 17 illustrates a configuration example of the light emitting deviceS0. The light emitting device S0 includes a light-guiding plate 120 anda prism sheet 140.

The light-guiding plate 120 is a substantially rectangularparallelepiped member having a pair of main surfaces (a front surfaceand a back surface) facing each other in the Z-axis direction (thefront-back direction), and four end surfaces (side surfaces) linkingfour sides of one of the main surfaces to four sides of the other. Amongthe four end surfaces, two surfaces facing each other in the X-axisdirection (the lateral direction) are light entering surfaces 120A and120B. Further, of the pair of main surfaces, the front surface is alight outgoing surface 120C, and the back surface is a light outgoingsurface 120D.

Lenses each having a triangular cross-sectional shape in the YZ planeand extending in the X-axis direction are provided on the light outgoingsurface 120C (the front surface) of the light-guiding plate 120, asillustrated in FIG. 17. These lenses are arranged side by side in theY-axis direction. The lenses each have an apex angle of 120 degrees, anda pitch of the lenses in the Y-axis direction is 0.1 [mm].

Further, a plurality of prisms PA are formed on the light outgoingsurface 120D (the back surface) of the light-guiding plate 120. Theprism PA has a gentle slope angle θ1 of 0.15 degrees, which is constantregardless of the X-axis coordinates. Furthermore, the prism PA has asteep slope angle θ2 of 70 degrees, which is constant regardless of theX-axis coordinates. The prism PA has a width LA of 0.2 [mm], which isconstant regardless of the X-axis coordinates. Hence, a height HA of theprism PA is also constant regardless of the X-axis coordinates.Moreover, a thickness D of the light-guiding plate 20 is also constantregardless of the X-axis coordinates.

A plurality of prisms Q are formed on a light entering surface 140A (aback surface) of the prism sheet 140. The prism Q has a symmetric shapein the X-axis direction, and an apex angle of 68 degrees.

FIG. 18 illustrates horizontal viewing angle characteristics in thelight emitting device S0. FIG. 19 illustrates horizontal viewing anglecharacteristics in a state where the prism sheet 140 is removed from thelight emitting device S0. Characteristics WA1 and WA2 indicate viewingangle characteristics in a case where the light source 10A emits light,and characteristics WB1 and WB2 indicate viewing angle characteristicsin a case where the light source 10B emits light. In the state where theprism sheet 140 is removed from the light emitting device S0, thecharacteristic WA1 has a peak at an observation angle around −80degrees, and the characteristic WB2 has a peak at an observation anglearound 60 degrees, as illustrated in FIG. 19. In contrast, when theprism sheet 140 is attached, the characteristics WA2 and WB2 each have apeak at an observation angle around 0 degrees. At this moment, thecharacteristic WB2 has a width substantially the same as a width of thecharacteristic WA2. In other words, a case where the plurality of lightsources 10B emit light (the characteristic WB2) is substantially thesame as a case where the plurality of light sources 10A emit light (thecharacteristic WA2), in terms of spread of light-outgoing directions.

(Light Emitting Device S1)

The light emitting device S1 corresponds to the light emitting device S0with the exception that the light-guiding plate 120 is replaced with alight-guiding plate 220. As with the light-guiding plate 120 (FIG. 17),lenses each having a triangular cross-sectional shape in the YZ planeand extending in the X-axis direction are arranged side by side in theY-axis direction, on a light outgoing surface 220C (a front surface) ofthe light-guiding plate 220. In addition, a plurality of prisms PA areformed on a light outgoing surface 220D (a back surface) of thelight-guiding plate 220. The prism PA has a gentle slope angle θ1 of0.15 degrees, which is constant regardless of the X-axis coordinates. Inaddition, the prism PA has a steep slope angle θ2 of 49 degrees, whichis constant regardless of the X-axis coordinates. The prism PA also hasa width LA of is 0.2 [mm], which constant regardless of the X-axiscoordinates. Hence, a height HA of the prism PA is also constantregardless of the X-axis coordinates. In addition, a thickness D of thelight-guiding plate 20 is also constant regardless of the X-axiscoordinates.

FIG. 20 illustrates horizontal viewing angle characteristics in thelight emitting device S1. A characteristic WA3 is a viewing anglecharacteristic in a case where the light source 10A emits light, and acharacteristic WB3 is a viewing angle characteristic in a case where thelight source 10B emits light. The characteristic WA3 is similar to thatin the light emitting device S0 (FIG. 18). In contrast, in thecharacteristic WB3, a luminous intensity is high at observation anglesaround −40 degrees and around 40 degree, as compared with the lightemitting device S0 (FIG. 18). In this way, in the light emitting deviceS1, the steep slope angle θ2 of the prism PA is set to 49 degrees, andtherefore it is possible to widen the range of light-outgoing directions(decrease the directivity) in a case where the plurality of lightsources 10B emit light.

(Light Emitting Device S2)

The light emitting device S2 corresponds to the light emitting device S1with the exception that the light-guiding plate 220 is replaced with alight-guiding plate 320. As with the light-guiding plate 120 (FIG. 17),lenses each having a triangular cross-sectional shape in the YZ planeand extending in the X-axis direction are arranged side by side in theY-axis direction, on a light outgoing surface 320C (a front surface) ofthe light-guiding plate 320. In addition, a plurality of prisms PA areformed on a light outgoing surface 320D (a back surface) of thelight-guiding plate 320. The prism PA has a shape similar to that in thelight emitting device 1 according to the present embodiment.

FIGS. 21A and 21B each illustrate distribution of luminance in the lightemitting device S2 in a case where the light source 10A emits light.FIG. 21A illustrates surface distribution of luminance, and FIG. 21Billustrates distribution of luminance in the horizontal direction. FIGS.22A and 22B each illustrate distribution of luminance in the lightemitting device S2 in a case where the light source 10B emits light.FIG. 22A illustrates surface distribution of luminance, and FIG. 22Billustrates distribution of luminance in the horizontal direction. InFIGS. 21A, 21B, 22A, and 22B, a right end corresponds to a side on whichthe plurality of light sources 10A are disposed, whereas a left endcorresponds to a side on which the plurality of light sources 10B aredisposed. FIGS. 21B and 22B illustrate characteristics WA5 and WB5 ofthe light emitting device S1, in addition to characteristics WA4 and WB4of the light emitting device S2.

In a case where the light source 10A emits light, the luminancedistribution in the horizontal direction (the characteristic WA4)spreads in a range wider than that in the light emitting device S1 (thecharacteristic WA5), as illustrated in FIG. 21B. In addition, in a casewhere the light source 10B emits light, the luminance distribution inthe horizontal direction (the characteristic WB4) is flatter than thatin the light emitting device S1 (the characteristic WB5), as illustratedin FIG. 22B. In this way, in the light emitting device S2, the shape ofthe prism PA changes depending on the X-axis coordinates, and thereforeit is possible to enhance uniformity of the luminance distribution.

(Light Emitting Device S3)

The light emitting device S3 corresponds to the light emitting device S2with the exception that the light-guiding plate 320 is replaced with alight-guiding plate 420. As with the light-guiding plate 120 (FIG. 17),lenses each having a triangular cross-sectional shape in the YZ planeand extending in the X-axis direction are arranged side by side in theY-axis direction, on a light outgoing surface 420C (a front surface) ofthe light-guiding plate 420. In addition, a plurality of prisms PA aswell as a plurality of prisms PB are formed on a light outgoing surface420D (a back surface) of the light-guiding plate 420. The prisms PA andPB each have a shape similar to that in the light emitting device 1according to the present embodiment.

FIGS. 23A and 23B each illustrate distribution of luminance in the lightemitting device S3 in a case where the light source 10A emits light.FIG. 23A illustrates surface distribution of luminance, and FIG. 23Billustrates distribution of luminance in the horizontal direction. FIGS.24A and 24B each illustrate distribution of luminance in the lightemitting device S3 in a case where the light source 10B emits light.FIG. 24A illustrates surface distribution of luminance, and FIG. 24Billustrates distribution of luminance in the horizontal direction. InFIGS. 23A, 23B, 24A, and 24B, a right end corresponds to a side on whichthe plurality of light sources 10A are disposed, whereas a left endcorresponds to a side on which the plurality of light sources 10B aredisposed. FIGS. 23B and 24B illustrate characteristics WA6 and WB6 ofthe light emitting device S3, and the characteristics WA4 and WB4 of thelight emitting device S2.

In a case where the light source 10A emits light, the luminancedistribution in the horizontal direction (the characteristic WA6)spreads in a range wider and flatter than that in the light emittingdevice S2 (the characteristic WA4), as illustrated in FIG. 23B.Specifically, the luminance on the side on which the plurality of lightsources 10A are disposed (the right end) is greater than that in thelight emitting device S2. In addition, in a case where the light source10B emits light, the luminance distribution in the horizontal direction(the characteristic WB6) spreads in a range wider than that in the lightemitting device S2 (the characteristic WB4), as illustrated in FIG. 24B.In this way, in the light emitting device S3, the prisms PB are providedand therefore it is possible to enhance the uniformity of the luminancedistribution further.

FIG. 25A illustrates surface distribution of luminance in proximity tothe light source 10A in a case where the light source 10A emits light.FIG. 25B illustrates surface distribution of luminance in proximity tothe light source 10B in a case where the light source 10B emits light.In FIG. 25A, a right end corresponds to a side on which the plurality oflight sources 10A are disposed. Similarly, in FIG. 25B, a left endcorresponds to a side on which the plurality of light sources 10B aredisposed. In a case where the light source 10A emits light, luminancedistribution (a so-called hotspot) corresponding to each of theplurality of light sources 10A appears in proximity to the plurality oflight sources 10A, as illustrated in FIG. 25A. Similarly, in a casewhere the light source 10B emits light, luminance distributioncorresponding to each of the plurality of light sources 10B appears inproximity to the plurality of light sources 10B, as illustrated in FIG.25B. In the light emitting device S4 to be described below, this hotspotis less noticeable.

(Light Emitting Device S4)

The light emitting device S4 corresponds to the light emitting device S3with the exception that the light-guiding plate 420 is replaced with thelight-guiding plate 20 according to the present embodiment. Thelight-guiding plate 20 corresponds to the light-guiding plate 420 withthe exception that the light outgoing surface 420C (the front surface)has the lenticular shape (FIG. 1).

FIG. 26A illustrates surface distribution of luminance in proximity tothe light source 10A in a case where the light source 10A emits light.FIG. 26B illustrates surface distribution of luminance in proximity tothe light source 10B in a case where the light source 10B emits light.In FIG. 26A, a right end corresponds to a side on which the plurality oflight sources 10A are disposed. Similarly, in FIG. 26B, a left endcorresponds to a side on which the plurality of light sources 10B aredisposed.

In a case where the light source 10A emits light, luminance distribution(a so-called hotspot) corresponding to each of the plurality of lightsources 10A appears in proximity to the plurality of light sources 10A,as illustrated in FIG. 26A. Similarly, in a case where the light source10B emits light, luminance distribution corresponding to each of theplurality of light sources 10B appears in proximity to the plurality oflight sources 10B, as illustrated in FIG. 26B. A horizontal length ofthe hotspot is shorter than that in the light emitting device S3 (FIGS.25A and 25B). In this way, in the light emitting device S4, the lightoutgoing surface 20C (the front surface) of the light-guiding plate 20has the lenticular shape, and therefore it is possible to make thehotspot less noticeable.

FIG. 27 illustrates horizontal viewing angle characteristics in thelight emitting device S4. A characteristic WA7 is a viewing anglecharacteristic in a case where the light source 10A emits light, and acharacteristic WB7 is a viewing angle characteristic in a case where thelight source 10B emits light. In this way, in the light emitting deviceS4, it is possible to narrow the range of light-outgoing directions(increase the directivity) in a case where the plurality of lightsources 10A emit light, and to widen the range of light-outgoingdirections (decrease the directivity) in a case where the plurality oflight sources 10B emit light, as with the light emitting device such asthe light emitting device S1 (FIG. 20). In the light emitting device S5to be described below, the viewing angle characteristics in a case wherethe plurality of light sources 10B emit light are improved.

(Light Emitting Device S5)

The light emitting device S5 corresponds to the light emitting device S4with the exception that the prism sheet 140 is replaced with the prismsheet 40 according to the present embodiment. The plurality of prisms Qeach having the asymmetry shape in the X-axis direction are formed onthe light entering surface 40A of the prism sheet 40, as illustrated inFIG. 10.

FIG. 28 illustrates horizontal viewing angle characteristics in thelight emitting device S5. A characteristic WA8 is a viewing anglecharacteristic in a case where the light source 10A emits light, and acharacteristic WB8 is a viewing angle characteristic in a case where thelight source 10B emits light. The characteristic WA8 is similar to thatin the light emitting device S4 (FIG. 27). In contrast, thecharacteristic WB8 has a high luminous intensity at an observation anglearound −20 degrees (FIG. 27), as compared with the light emitting deviceS4. In this way, in the light emitting device S5, the plurality ofprisms Q each having the asymmetry shape are used, and therefore it ispossible to improve the viewing angle characteristics in a case wherethe plurality of light sources 10B emit light.

In addition, by further providing the diffusing sheet 50 in the lightemitting device S5, it is possible to improve the viewing anglecharacteristics further as illustrated in FIG. 15.

(About Steep Slope Angle θ2)

In the light emitting device 1, the steep slope angle θ2 is 49 degrees.This allows the light emitting device 1 to widen the range oflight-outgoing directions (decrease the directivity) in a case where theplurality of light sources 10B emit light, as described by way ofexample above using each of the light emitting devices S0 and S1according to the respective reference examples. Viewing anglecharacteristics in a case where the steep slope angle θ2 is changedrelative to that in the light emitting device S1 according to thereference example will be described below.

FIGS. 29A to 29F each illustrate horizontal viewing anglecharacteristics. FIG. 29A illustrates a case where the steep slope angleθ2 is 70 degrees (i.e., the light emitting device S0). FIG. 29Billustrates a case where the steep slope angle θ2 is 59 degrees. FIG.29C illustrates a case where the steep slope angle θ2 is 49 degrees(i.e., the light emitting device S2). FIG. 29D illustrates a case wherethe steep slope angle θ2 is 39 degrees. FIG. 29E illustrates a casewhere the steep slope angle θ2 is 19 degrees. FIG. 29F illustrates acase where the steep slope angle θ2 is 9 degrees. Characteristics WA11to WA16 are viewing angle characteristics in a case where the pluralityof light sources 10A emit light, and characteristics WB11 the WB16 areviewing angle characteristics in a case where the plurality of lightsources 10B emit light.

In the case where the steep slope angle θ2 is 70 degrees (FIG. 29A),spread of light-outgoing directions in the characteristic WB11 in a casewhere the plurality of light sources 10B emit light is substantially thesame as that of the characteristic WA11 in a case where the plurality oflight sources 10A emit light. In the case where the steep slope angle θ2is 59 degrees (FIG. 29B), luminous intensity in the characteristic WB12is high at observation angles around −50 degrees and around 30 degrees.At the time, the luminous intensity is high on a negative observationangles side.

In contrast, in the case where the steep slope angle θ2 is 39 degrees(FIG. 29D), the luminous intensity is high at observation angles around−40 degrees and around 40 degrees in the characteristic WB14. At thetime, the luminous intensity is high on a positive observation anglesside. In the case where the steep slope angle θ2 is 19 degrees (FIG.29E), the characteristic WB15 indicates a state where a plurality ofpeaks appearing in the case of FIG. 29D are about to unify. In the casewhere the steep slope angle θ2 is 9 degrees (FIG. 29F), in thecharacteristic WB16, the plurality of peaks appearing in the case ofFIG. 29D unify, and the range of light-outgoing directions is slightlywider than that in the characteristic WA16.

For these reasons, the steep slope angle θ2 is, for example, desirably19 degrees or more and 59 degrees or less, and in particular, morepreferably, 39 degrees or more and 59 degrees or less. This allows thelight emitting device 1 to widen the range of light-outgoing directions(decrease the directivity) in a case where the plurality of lightsources 10B emit light.

[Effects]

As described above, in the present embodiment, the light source sectionincluding the plurality of light sources 10A and the light sourcesection including the plurality of light sources 10B are configured toemit light individually. It is therefore possible to change thedirectivity between the case where the plurality of light sources 10Aemit light and the case where the plurality of light sources 10B emitlight.

In the present embodiment, the steep slope angle θ2 of the prism PA isset to be around 49 degrees. It is therefore possible to widen the rangeof light-outgoing directions (decrease the directivity) in a case wherethe plurality of light sources 10B emit light.

In the present embodiment, the shape of the prism PA changes dependingon the X-axis coordinates, and therefore it is possible to enhance theuniformity of the luminance distribution. Moreover, the prism PB isprovided in addition to the prism PA. This makes it possible to enhancethe uniformity of the luminance distribution further.

In the present embodiment, the light outgoing surface 20C (the frontsurface) of the light-guiding plate 20 has the lenticular shape. Thismakes it possible to make the hotspot less noticeable.

In the present embodiment, the prism sheet having the plurality ofprisms Q each having the asymmetry shape is provided. It is thereforepossible to improve the viewing angle characteristics, in a case wherethe plurality of light sources 10B emit light. In addition, thediffusing sheet 50 is further provided, which makes it possible toimprove the viewing angle characteristics further.

[Modification Example]

In the above-described embodiment, the light outgoing surface 20C of thelight-guiding plate 20 faces the prism sheet 40, and the light outgoingsurface 20D faces the reflection sheet 30, but this is not limitative.Instead of this, for example, the light-guiding plate 20 may be reversedto have the light outgoing surface 20D facing the prism sheet 40 and thelight outgoing surface 20C facing the reflection sheet 30, as with alight emitting device 1B illustrated in FIG. 30.

2. Second Embodiment

Next, a display unit 2 according to a second embodiment will bedescribed. The display unit 2 is a liquid crystal display unit in whichthe light emitting device 1 is used as a backlight.

FIG. 31 illustrates a configuration example of the display unit 2according to the second embodiment. The display unit 2 includes a liquidcrystal display section 9 and the light emitting device 1. The lightemitting device 1 is disposed on a back surface side of the liquidcrystal display section 9.

The liquid crystal display section 9 is a transmission liquid crystaldisplay section, and a plurality of pixels Pix not illustrated arearranged in a matrix. Further, the liquid crystal display section 9modulates light emitted from the light emitting device 1 on the basis ofa supplied image signal. An image is thereby displayed in the displayunit 2.

As described in the first embodiment, the light emitting device 1 isallowed to change the directivity between the case where the pluralityof light sources 10A emit light and the case where the plurality oflight sources 10B emit light. This allows the display unit 2 to performdisplay by narrowing a viewing angle in a case where the plurality oflight sources 10A emit light and to perform display by widening theviewing angle in a case where the plurality of light sources 10B emitlight.

3. Application Examples

Next, application examples of the light emitting device described ineach of the above-described embodiments and modification example will bedescribed.

FIG. 32A illustrates an appearance of an electronic book to which thelight emitting device of any of the above-described embodiments and thelike is applied. FIG. 32B illustrates an appearance of anotherelectronic book to which the light emitting device of any of theabove-described embodiments and the like is applied. These electronicbooks each have, for example, a display section 210 and a non-displaysection 220. The display section 210 is configured of, for example, aliquid-crystal display panel in which the light emitting deviceaccording to any of the above-described embodiments and the like is usedas a backlight.

FIG. 33 illustrates an appearance of a smartphone to which the lightemitting device of any of the above-described embodiments and the likeis applied. This smartphone has, for example, a display section 230 anda non-display section 240. The display section 230 is configured of, forexample, a liquid-crystal display panel in which the light emittingdevice according to any of the above-described embodiments and the likeis used as a backlight.

The light emitting device of any of the above-described embodiments andthe like is applicable to electronic apparatuses in various fields.Examples of the electronic apparatuses include television apparatusesand laptop personal computers, in addition to the above-describedelectronic books and smartphone.

FIG. 34 illustrates an appearance of an illumination unit for indooruse, to which the light emitting device of any of the above-describedembodiments and the like is applied. This illumination unit has, forexample, an illumination section 844 configured of the light emittingdevice according to any of the above-described embodiments and the like.Any number of the illumination sections 844 are disposed at any intervalon a ceiling 850A of a building. It is to be noted that it is possibleto install the illumination section 844 at any position such as a wall850B and a floor (not illustrated) depending on an intended use, withoutbeing limited to the ceiling 850A.

Such electronic apparatuses and illumination unit each performillumination by using light from the light emitting device. It ispossible to change directivity during the illumination. For example, inapplication to a car navigation system, it is possible to prevent adisplayed image from being viewed by a driver, by narrowing the range oflight-outgoing directions while driving, for example. Further, inapplication to an illumination unit, it is possible to use theillumination unit as an ordinary illuminator by widening the range oflight-outgoing directions, and to use the illumination unit as, forexample, a spotlight or an indirect illuminator by narrowing the rangeof light-outgoing directions. In this way, it is possible to implementvarious functions by applying the light emitting device of any of theabove-described embodiments and the like to electronic apparatuses andillumination units.

The technology is described above using the embodiments and themodification example, as well as the application examples of applicationto electronic apparatus. However, the technology is not limited to theseembodiments and the like, and is variously modifiable. For example, thevarious parameters described in the embodiments are not limitative, andany of numerical values of the respective parameters may be changed asappropriate.

In addition, for example, in the above-described embodiments, the lightsources 10A and 10B are each configured using the light emitting diode,but this is not limitative. For example, the light sources may each beconfigured using a cold cathode fluorescent lamp (CCFL), in place of thelight emitting diode.

Moreover, for example, the configuration of each of the light emittingdevices is specifically described above in the embodiments and the like.However, it is not necessary to provide all components, and othercomponent may be provided.

It is to be noted that the effects described herein are mere exampleswithout being limitative, and other effects may also be provided.

It is to be noted that the technology may adopt the followingconfigurations.

(1) A light emitting device including:

a first light source and a second light source;

a light-guiding plate having a first main surface, a second mainsurface, a first end surface, and a second end surface, the first mainsurface and the second main surface facing each other, the first endsurface facing the first light source, the second end surface facing thefirst end surface and the second light source;

a prism sheet disposed to face the first main surface; and

a reflection sheet disposed to face the second main surface,

the light-guiding plate including a plurality of first slope sectionsand a plurality of second slope sections both provided on one of thefirst main surface and the second main surface,

the plurality of first slope sections being provided to allow thelight-guiding plate to be thinner in a first direction that extends fromthe first end surface to the second end surface,

the plurality of second slope sections being provided to allow thelight-guiding plate to be thicker in the first direction, and each beingprovided alternately with each of the first slope sections in the firstdirection, and

a proportion of area occupied by the plurality of second slope sectionsincreasing in a predetermined range from the second end surface, as adistance from the second end surface increases.

(2) The light emitting device according to (1), in which a level ofinclination of any of the first slope sections is smaller than a levelof inclination of any of the second slope sections.

(3) The light emitting device according to (1) or (2), in which thelight-guiding plate includes a third slope section and a fourth slopesection both provided in each of regions in which a predetermined numberof first slope sections of the plurality of first slope sections areprovided,

the third slope section being provided to allow the light-guiding plateto be thinner in the first direction, and

the fourth slope section being provided to allow the light-guiding plateto be thicker in the first direction.

(4) The light emitting device according to (3), in which a level ofinclination of the third slope section is smaller than a level ofinclination of the fourth slope section.

(5) The light emitting device according to (3) or (4), in which a levelof inclination of the third slope section is greater than a level ofinclination of the first slope section.

(6) The light emitting device according to any one of (3) to (5), inwhich a proportion of area, occupied by the third slope section in eachof the regions in which the predetermined number of first slope sectionsare provided, decreases as a distance from the first end surfaceincreases.

(7) The light emitting device according to any one of (3) to (6), inwhich the third slope section and the fourth slope section are providedin a predetermined range from the first end surface.

(8) The light emitting device according to any one of (1) to (7), inwhich an inclination angle of any of the second slope sections is in arange from 19 degrees to 59 degrees.

(9) The light emitting device according to (8), in which the inclinationangle is in a range from 39 degrees to 59 degrees.

(10) The light emitting device according to any one of (1) to (9), inwhich the light-guiding plate further includes a lenticular lensdisposed on another one of the first main surface and the second mainsurface which is different from the one of the first main surface andthe second main surface on which the plurality of first slope sectionsand the plurality of second slope sections are provided.

(11) The light emitting device according to (10), in which thelenticular lens includes a plurality of lenses extending in the firstdirection and disposed side by side in a second direction thatintersects the first direction.

(12) The light emitting device according to any one of (1) to (11), inwhich the prism sheet includes a plurality of prisms extending in asecond direction that intersects the first direction, and disposed sideby side in the first direction.

(13) The light emitting device according to (12), in which the prismseach have an asymmetry shape in the first direction.

(14) The light emitting device according to (12) or (13), in which

the prisms each have a ridge, a first surface, and a second surface, theridge extending in the second direction, the first surface and thesecond surface being provided with the ridge in between,

an angle between the first surface and the second surface is an acuteangle, and

one or both of the first surface and the second surface have a changinginclination.

(15) The light emitting device according to (14), in which

the first surface is a surface disposed on a side on which the firstlight source is provided,

the second surface is a surface disposed on a side on which the secondlight source is provided, and

the first surface has a greater change in inclination than a change ininclination of the second surface.

(16) The light emitting device according to any one of (1) to (15), inwhich the first light source and the second light source are allowed toemit light individually.

(17) The light emitting device according to any one of (1) to (16), inwhich the plurality of first slope sections and the plurality of secondslope sections are provided on the first main surface.

(18) The light emitting device according to any one of (1) to (16), inwhich the plurality of first slope sections and the plurality of secondslope sections are provided on the second main surface.

(19) A display unit with a liquid crystal display section and alight-emission section, the light-emission section being disposed on aback surface side of the liquid crystal display section, thelight-emission section including:

a first light source and a second light source;

a light-guiding plate having a first main surface, a second mainsurface, a first end surface, and a second end surface, the first mainsurface and the second main surface facing each other, the first endsurface facing the first light source, the second end surface facing thefirst end surface and the second light source;

a prism sheet disposed to face the first main surface; and

a reflection sheet disposed to face the second main surface,

the light-guiding plate including a plurality of first slope sectionsand a plurality of second slope sections both provided on one of thefirst main surface and the second main surface,

the plurality of first slope sections being provided to allow thelight-guiding plate to be thinner in a first direction that extends fromthe first end surface to the second end surface,

the plurality of second slope sections being provided to allow thelight-guiding plate to be thicker in the first direction, and each beingprovided alternately with each of the first slope sections in the firstdirection, and

a proportion of area occupied by the plurality of second slope sectionsincreasing in a predetermined range from the second end surface, as adistance from the second end surface increases.

(20) An illumination unit with a light emitting device, the lightemitting device including:

a first light source and a second light source;

a light-guiding plate having a first main surface, a second mainsurface, a first end surface, and a second end surface, the first mainsurface and the second main surface facing each other, the first endsurface facing the first light source, the second end surface facing thefirst end surface and the second light source;

a prism sheet disposed to face the first main surface; and

a reflection sheet disposed to face the second main surface,

the light-guiding plate including a plurality of first slope sectionsand a plurality of second slope sections both provided on one of thefirst main surface and the second main surface,

the plurality of first slope sections being provided to allow thelight-guiding plate to be thinner in a first direction that extends fromthe first end surface to the second end surface,

the plurality of second slope sections being provided to allow thelight-guiding plate to be thicker in the first direction, and each beingprovided alternately with each of the first slope sections in the firstdirection, and

a proportion of area occupied by the plurality of second slope sectionsincreasing in a predetermined range from the second end surface, as adistance from the second end surface increases.

The present application is based on and claims priority from JapanesePatent Application No. 2014-253646 filed with the Japan Patent Office onDec. 16, 2014, the entire contents of which is hereby incorporated byreference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A light emitting device comprising: a first light source and a secondlight source; a light-guiding plate having a first main surface, asecond main surface, a first end surface, and a second end surface, thefirst main surface and the second main surface facing each other, thefirst end surface facing the first light source, the second end surfacefacing the first end surface and the second light source; a prism sheetdisposed to face the first main surface; and a reflection sheet disposedto face the second main surface, the light-guiding plate including aplurality of first slope sections and a plurality of second slopesections both provided on one of the first main surface and the secondmain surface, the plurality of first slope sections being provided toallow the light-guiding plate to be thinner in a first direction thatextends from the first end surface to the second end surface, theplurality of second slope sections being provided to allow thelight-guiding plate to be thicker in the first direction, and each beingprovided alternately with each of the first slope sections in the firstdirection, and a proportion of area occupied by the plurality of secondslope sections increasing in a predetermined range from the second endsurface, as a distance from the second end surface increases.
 2. Thelight emitting device according to claim 1, wherein a level ofinclination of any of the first slope sections is smaller than a levelof inclination of any of the second slope sections.
 3. The lightemitting device according to claim 1, wherein the light-guiding plateincludes a third slope section and a fourth slope section both providedin each of regions in which a predetermined number of first slopesections of the plurality of first slope sections are provided, thethird slope section being provided to allow the light-guiding plate tobe thinner in the first direction, and the fourth slope section beingprovided to allow the light-guiding plate to be thicker in the firstdirection.
 4. The light emitting device according to claim 3, wherein alevel of inclination of the third slope section is smaller than a levelof inclination of the fourth slope section.
 5. The light emitting deviceaccording to claim 3, wherein a level of inclination of the third slopesection is greater than a level of inclination of the first slopesection.
 6. The light emitting device according to claim 3, wherein aproportion of area, occupied by the third slope section in each of theregions in which the predetermined number of first slope sections areprovided, decreases as a distance from the first end surface increases.7. The light emitting device according to claim 3, wherein the thirdslope section and the fourth slope section are provided in apredetermined range from the first end surface.
 8. The light emittingdevice according to claim 1, wherein an inclination angle of any of thesecond slope sections is in a range from 19 degrees to 59 degrees. 9.The light emitting device according to claim 8, wherein the inclinationangle is in a range from 39 degrees to 59 degrees.
 10. The lightemitting device according to claim 1, wherein the light-guiding platefurther includes a lenticular lens disposed on another one of the firstmain surface and the second main surface which is different from the oneof the first main surface and the second main surface on which theplurality of first slope sections and the plurality of second slopesections are provided.
 11. The light emitting device according to claim10, wherein the lenticular lens includes a plurality of lenses extendingin the first direction and disposed side by side in a second directionthat intersects the first direction.
 12. The light emitting deviceaccording to claim 1, wherein the prism sheet includes a plurality ofprisms extending in a second direction that intersects the firstdirection, and disposed side by side in the first direction.
 13. Thelight emitting device according to claim 12, wherein the prisms eachhave an asymmetry shape in the first direction.
 14. The light emittingdevice according to claim 12, wherein the prisms each have a ridge, afirst surface, and a second surface, the ridge extending in the seconddirection, the first surface and the second surface being provided withthe ridge in between, an angle between the first surface and the secondsurface is an acute angle, and one or both of the first surface and thesecond surface have a changing inclination.
 15. The light emittingdevice according to claim 14, wherein the first surface is a surfacedisposed on a side on which the first light source is provided, thesecond surface is a surface disposed on a side on which the second lightsource is provided, and the first surface has a greater change ininclination than a change in inclination of the second surface.
 16. Thelight emitting device according to claim 1, wherein the first lightsource and the second light source are allowed to emit lightindividually.
 17. The light emitting device according to claim 1,wherein the plurality of first slope sections and the plurality ofsecond slope sections are provided on the first main surface.
 18. Thelight emitting device according to claim 1, wherein the plurality offirst slope sections and the plurality of second slope sections areprovided on the second main surface.
 19. A display unit with a liquidcrystal display section and a light-emission section, the light-emissionsection being disposed on a back surface side of the liquid crystaldisplay section, the light-emission section comprising: a first lightsource and a second light source; a light-guiding plate having a firstmain surface, a second main surface, a first end surface, and a secondend surface, the first main surface and the second main surface facingeach other, the first end surface facing the first light source, thesecond end surface facing the first end surface and the second lightsource; a prism sheet disposed to face the first main surface; and areflection sheet disposed to face the second main surface, thelight-guiding plate including a plurality of first slope sections and aplurality of second slope sections both provided on one of the firstmain surface and the second main surface, the plurality of first slopesections being provided to allow the light-guiding plate to be thinnerin a first direction that extends from the first end surface to thesecond end surface, the plurality of second slope sections beingprovided to allow the light-guiding plate to be thicker in the firstdirection, and each being provided alternately with each of the firstslope sections in the first direction, and a proportion of area occupiedby the plurality of second slope sections increasing in a predeterminedrange from the second end surface, as a distance from the second endsurface increases.
 20. An illumination unit with a light emittingdevice, the light emitting device comprising: a first light source and asecond light source; a light-guiding plate having a first main surface,a second main surface, a first end surface, and a second end surface,the first main surface and the second main surface facing each other,the first end surface facing the first light source, the second endsurface facing the first end surface and the second light source; aprism sheet disposed to face the first main surface; and a reflectionsheet disposed to face the second main surface, the light-guiding plateincluding a plurality of first slope sections and a plurality of secondslope sections both provided on one of the first main surface and thesecond main surface, the plurality of first slope sections beingprovided to allow the light-guiding plate to be thinner in a firstdirection that extends from the first end surface to the second endsurface, the plurality of second slope sections being provided to allowthe light-guiding plate to be thicker in the first direction, and eachbeing provided alternately with each of the first slope sections in thefirst direction, and a proportion of area occupied by the plurality ofsecond slope sections increasing in a predetermined range from thesecond end surface, as a distance from the second end surface increases.